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Lead-Free Solder Joints under Thermal Stress-Reliability Study, Mechanism Discussion, and Improvement Strategy Analysis(I)
|作者:||陳志銘||關鍵字:||應用研究;Lead-free solder joint;材料科技;無鉛銲點;應力;界面反應;錫鬚;Stress;Interfacial reactions;Tin whisker||摘要:||
隨著電子產品綠化之浪潮，銲點之無鉛化受到相當大之注目，亦引起廣泛之研究討論，其中界面反應與錫鬚等兩項議題由於與銲點之可靠度息息相關，因此最受到重視。本計畫主要探討應力於銲點生成後，對於上述兩種現象之影響。初期覆晶銲點之發展，主要將晶片連接至陶瓷基板上，而為了減輕封裝重量與成本考量，逐漸將陶瓷基板轉換成塑膠基板。然而，此項材料之變動卻造成銲點處之應力集中，這是由於矽晶片與塑膠基板間之熱膨脹係數差異過大(2.3 ppm/℃ vs. 18 ppm/℃)，使得當電流訊號通過銲點時，引起之熱使得矽晶片與塑膠基板熱膨脹之情況不同，而造成銲點之變形，使其處於應力作用之環境下，此時，銲點內部之界面反應除了受到加熱影響外，同時也受到應力之影響。由於應力具有改變元素擴散行為之能力，因此預期對於界面反應與錫鬚成長勢必會造成影響，尤其隨著覆晶銲點朝更小尺寸之發展，銲點處應力之影響將愈形重要。然而，文獻中對於應力影響之報告寥寥可數，而此數據之缺乏將增加銲點可靠度評估時之不確定性，因此本計畫之實施有其重要性與迫切性。根據申請人先期之研究顯示，應力確實會對常見之Sn/Cu 系統界面反應造成影響，而更深入之探討與對其他銲點系統(Sn/Ag 與Sn/Ni)之研究則是本計畫申請之主要原因。
With the green trend of the electronic products, the lead-free trend of the solder jointsreceives much attention and lots of efforts have been devoted to this. The most importanttwo issues are interfacial reactions and tin whiskers because both are crucial factors to thejoint reliabilities. This project aims to investigate the effects of stress formed at the solderjoints on the above-mentioned two phenomena. In the past, the flip-chip technology usedceramic materials as the substrate for the chip bonding. The ceramic substrates weregradually replaced by the plastic substrates in order to reduce the packaging weight and thecost. However, this change of substrate materials results in the thermal stress concentrated inthe solder joints. This is due to the large mismatch of the coefficient of thermal expansionbetween the Si chip and the plastic substrates (2.3 ppm/℃ vs. 18 ppm/℃). Therefore, thesolder joints simultaneously suffer the heating and stress impacts. Because the stress can alsoinfluence the diffusion ability of the atoms, it is expectable that the stress can also affect theinterfacial reactions and Sn whisker growth in the solder joints. The effects of stress willbecome more and more significant especially for smaller solder joints. However, relatedreferences are rarely found, which in turn reveals the importance and emergency of thisproject. According to the preliminary results, we have found that the stress indeed hassignificant effects on the Sn/Cu interfacial reactions. Further discussion and theinvestigations on other systems, like Sn/Ag and Sn/Ni, require the support of NationalScience Council, and this is also the reason for the application of this project.
|Appears in Collections:||化學工程學系所|
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